Chromosome X News and Research

The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million base pairs (the building blocks of DNA) and represents approximately 5 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in somatic cells (cells other than egg and sperm cells). This phenomenon is called X-inactivation or Lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Some genes on the X chromosome escape X-inactivation. These genes are located at the tip of the short (p) arm of the X chromosome in an area known as the pseudoautosomal region. Although many genes are unique to the X or Y chromosome, genes in the pseudoautosomal region are present on both chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal region are essential for normal development.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The X chromosome likely contains between 900 and 1,400 genes.

Genes on the X chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.

Further Reading

For the last two decades, researchers worldwide have been using whole genome sequencing to understand what makes cells radiation-resistant, hoping to solve an old biological mystery: why is it that one of the most radiation-resistant organisms, Deinococcus radiodurans, aka "Conan the bacterium," can survive hundreds of times more DNA damage caused by gamma rays than most other organisms? According to a study published recently in Standards of Genomic Sciences by researchers at the Uniformed Services University (USU), the amount of radiation a Deinococcus cell can survive in fact has little to do with the number and types of its DNA repair proteins.

A team of researchers led by a bioinformatician at the University of California San Diego has developed a method to help determine whether certain hard-to-study mutations in the human genome, called short tandem repeats or microsatellites, are likely to be involved in harmful conditions.

Each cell in the average human body contains 23 pairs of chromosomes, with four telomeres on each pair. Telomeres cover the end of the chromosome, protecting it from deterioration or fusion with adjacent chromosomes, much like the plastic tip at the end of a shoelace protects it from unraveling.

Schizophrenia is a complicated disease that often appears in early adulthood. Although scientists have not traced the genetic causes, more than 80% of schizophrenia cases are considered to have a hereditary cause.

A fertilized human egg develops into multiple tissues, organs and about 200 distinct cell types. Each cell type has the same genes, but they are expressed differently during development and in mature cells.

An international study of integrated HHV-6 has discovered that a small number of human ancestors, one from about 24,000 years ago, have been responsible for transmitting ancient strains of the virus to individuals today - affecting about a million people in the UK alone.

Scientists from the Children's Medical Center Research Institute at UT Southwestern have developed an innovative system to identify and characterize the molecular components that control the activities of regulatory DNA sequences in the human genome.

A mutation that helps make cells immortal is critical to the development of a tumor, but new research at the University of California, Berkeley suggests that becoming immortal is a more complicated process than originally thought.

An assay that identifies a peculiar but important abnormality in cancer cells has been developed and validated by researchers at The Ohio State University Comprehensive Cancer Center - Arthur G. James Cancer Hospital and Richard J. Solove Research Institute.

Aging is the continuing process of such stress exposures, and with advancing age (normal aging), we must carry lots of senescent cells within our bodies. Senescent cells also often provide some ‘bad influences’ to surrounding healthy cells; such as chronic inflammation and tumorigenesis

Natera, Inc. a leader in non-invasive genetic testing and the analysis of circulating cell-free DNA, today announced the publication of a large clinical experience study evaluating the performance of the company's Panorama® non-invasive prenatal test (NIPT).

There is much research that shows that therapy dogs can help reduce stress and improve emotional well-being in vulnerable individuals. Rachel McPherson talks about this research that the work done by The Good Dog Foundation.

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